Question: $ { \left[\begin{array}{rr}{1} & {-1} \\ {-2} & {2} \\ {3} & {1}\end{array}\right]+\left[\begin{array}{rr}{-2} & {-1} \\ {0} & {0} \\ {0} & {-2}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{1}+{-2} & {-1}+{-1} \\ {-2}+{0} & {2}+{0} \\ {3}+{0} & {1}+{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-1} & {-2} \\ {-2} & {2} \\ {3} & {-1}\end{array}\right]}$